This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-281339 filed Sep. 17, 2001.
1. Field of the Invention
The present invention relates to a pressure-changing device for a leak check system that checks for leaks in a fuel vapor treatment system by changing the pressure in the fuel vapor treatment system.
2. Description of Related Art
Conventionally, a known fuel vapor treatment system adsorbs fuel vapor forming in a fuel tank with adsorbent such as granulated active carbon contained in an adsorption vessel. The fuel vapor treatment system discharges the adsorbed fuel vapor into a suction pipe by negative pressure in the suction pipe. The fuel vapor treatment system should be checked for leaks because if it has a leak, the fuel vapor flows out to the environment. A known leak check system for the fuel vapor treatment system delivers air into the adsorption vessel with a pump to pressurize a fuel vapor path in the fuel treatment system. The fuel vapor path is a path through which the fuel vapor flows. A pressure sensor disposed in the fuel tank detects pressure in the fuel vapor path under pressurization, as the fuel tank is a part of the fuel vapor path. If pressure in the fuel vapor path is below a threshold pressure, the leak check system determines that the fuel vapor treatment system has a leak. After the leak check, the fuel vapor path is connected with the atmosphere to release pressure therein.
However, the pressure sensor is exposed to the fuel vapor, since it is disposed in the fuel tank or in the pipes where the fuel vapor forms or flows. Therefore, the pressure sensor needs be resistant to the fuel vapor to prevent corrosion, increasing the cost of the pressure sensor.
On the other hand, if the pressure sensor is attached to the fuel tank or the pipe, a connection between the pressure sensor and the fuel tank or the pipe needs some extra work to prevent a leak of the fuel vapor from the connection. As a result, installation cost of the pressure sensor is increased.
It is therefore an object of the present invention to provide an improved pressure-changing device in which a pressure sensor is protected from fuel vapor.
It is another object of the present invention to provide an improved pressure-changing device in which a pressure sensor is easy to install.
It is another object of the present invention to provide an improved pressure-changing device that detects pressure in a fuel vapor path without being affected by foreign materials in a communicating path through which a pump communicates with an electromagnetic valve.
It is yet another object of the present invention to provide an improved pressure-changing device that detects pressure in a fuel vapor path without being affected by pressure of a flow that passes between a pump and an electromagnetic valve.
According to an aspect of the present invention, a pressure device, a pressure-changing device, has a pump, an electromagnetic valve, and a pressure sensor disposed in a communicating path through which the pump communicates with the electromagnetic valve. When the electromagnetic valve connects the pump with an adsorption vessel, the communicating path interconnects with a fuel vapor path including the adsorption vessel. Accordingly, pressure in the fuel vapor path is determined by detecting the pressure in the communicating path.
In the construction, the adsorption vessel is disposed between the electromagnetic valve and the fuel tank. In addition, in a case in which the leak check is operated by pressurizing the fuel vapor path, the communicating path is connected with the fuel vapor path by the electromagnetic valve only when the pump delivers air into the fuel vapor path via the communicating path. Therefore, little or no fuel vapor flows into the communicating path. Accordingly, exposure of the pressure sensor to the fuel vapor is minimized. Thus, the pressure sensor is protected from the fuel vapor.
According to another aspect of the present invention, the communicating path is formed in an airtight housing of the pressure-changing device. Therefore, air-tightness at a connection between the pressure sensor and the housing of the pressure device is ensured without requiring extra work. Accordingly, the pressure sensor is easily installed.